Wikipedia:Reference desk/Archives/Science/2008 May 20

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May 20

Refractive Index

I need to know the refractive index of solid ozone and solid HCl at infrared wavelengths and at ~80 K. I have not been able to find them anywhere. Can anybody help me? Cheers. --Shniken1 (talk) 04:23, 20 May 2008 (UTC)

Just a wild guess, but if this is a homework assignment they might want you to calculate it, rather than look s.th. up. Look at Hydrogen chloride "Melting point -114.2°C (158.8 K)" "Boiling point -85.1°C (187.9 K)" also look at Refractive index, phase velocity and Infrared.--71.236.23.111 (talk) 04:41, 20 May 2008 (UTC)

Nah it's not homework. Surely there is a comprehensive table somewhere with refractive indicies. All I can find are tables with the refractive indicies of gemstones on them..--Shniken1 (talk) 05:01, 20 May 2008 (UTC)

Doesn't look like it. These authors complained that there wasn't [1] They supplied some data. This might have something on ozone [2] For this you'd need an American Institute of Physics password, it might be something worth looking at, or nothing of interest [[scitation.aip.org/protected/mdfeed/ScholarFeed-20060721_JCPSA6_64.xml]. Good luck. 71.236.23.111 (talk) 05:25, 20 May 2008 (UTC) (oops, darn bot)

Please explain why coefficient of kinetic friction is less than its static counterpart by referring to electromagnetic bonds

I had been under the impression that the reason it takes a greater force to start sliding something than to keep it moving was due to the jagged roughness (at an atomic level) of the surfaces. But if friction is due to electromagnetic bonds, then why does moving have anything to do with it? Is roughness irrelevant? Dicetumbler (talk) 04:37, 20 May 2008 (UTC)

I can speculate....

Perhaps it's because a moving object has momentum. In addition to the force required to keep the object moving, the object has an intrinsic force of m×g, where m is mass and g is the downward acceleration constant due to gravity (9.8 m/s²).

Or maybe, if an object is stationary, there are more electromagnetic bonds that form than when the object is moving and the bonds are continually being broken and re-formed. =Axlq 04:52, 20 May 2008 (UTC)

Question about the Alcubierre Drive theory

So about the Alcubierre_drive -- so if I'm getting this correctly, someone or something inside of the "warp bubble" would be unable to observe or interact with the area outside of the bubble. This leads to practical problems regarding steering and navigation. Okay. Got it. But supposing rather than the hypothetical spaceship inside of the bubble doing the driving, the bubble was merely generated around the ship, pointed in the right direction, and somehow made to deactivate or deteriorate after a given period of time? Or perhaps made to deteriorate in response to a given set of conditions, like entering the gravity well of a star? -- Call it the "warp cannon" or "warp rocket" approach. Is there anything in the theory (putting aside the known problems, like that pesky exotic matter) that would prevent this from working? Thanks. Please keep in mind when responding, I really don't know anything about physics, nor do I claim to. --Brasswatchman (talk) 06:16, 20 May 2008 (UTC)

There's nothing in the theory to prevent anything from working. General relativity relates the geometry of spacetime to the distribution of matter and energy in it, but it doesn't constrain the geometry. You can write down any crazy spacetime geometry you want and plug it into the equations of general relativity and it will tell you what the mass-energy distribution has to be. Alcubierre simply wrote down a geometry that roughly corresponds to the science-fiction idea of a warp drive, and then plugged it into general relativity to see what the mass-energy distribution looked like. The answer is that it looks like nothing known to science. It's not just that you need stuff with negative mass, it has to move over time in the way the warp drive demands, even though there are no laws of physics that would cause any kind of matter to move that way. That's where things should have ended, but for some reason they didn't, possibly because the desire to believe in warp drives is so strong and possibly because not everyone understands how little general relativity by itself can tell you about what is and isn't possible.

As for particular technologies like your cannon, there's only a limited amount of speculation you can do without inventing some laws of physics that would allow the drive to work in the first place. People who work on this stuff do make at least a couple of basic physical assumptions. One is no faster-than-light travel in the usual local sense, and the other is some limited form of causality to prevent the warp bubbles from showing up spontaneously for no reason. The second assumption is actually pretty dubious because the warp bubbles do show up spontaneously in Alcubierre's geometry, and if you invoke some physics to prevent that from happening, it's hard to see why it wouldn't also prevent the exotic matter from behaving in the right way once it's been introduced. But anyway, with those assumptions your cannon won't work. The outside of the bubble at later times is causally disconnected from the outside at earlier times, so (assuming no local FTL) it can't propagate on its own, and (assuming no acausal magic) the right configuration of exotic matter for continued propagation won't appear on its own. The closest you could get would be a cannon that starts firing long in advance, emitting a fast-moving configuration of matter that evolves into later stages of the warp drive in reverse order (the earliest matter fired becomes the last stage of the warp bubble). But it's only because we've discarded virtually every law of physics that we can even begin to contemplate such a thing. -- BenRG (talk) 10:50, 20 May 2008 (UTC)

The second assumption is actually pretty dubious because the warp bubbles do show up spontaneously in Alcubierre's geometry

Which in general doesn't match up with the observed universe. Okay, got it.

The outside of the bubble at later times is causally disconnected from the outside at earlier times, so (assuming no local FTL) it can't propagate on its own, and (assuming no acausal magic) the right configuration of exotic matter for continued propagation won't appear on its own.

Okay... let me try and get this straight. Causally disconnected... So things that might happen to the bubble at the beginning of its journey won't effect the state of the bubble at the end of its journey? Let's say, I don't know, someone spray-paints something on the front of the bubble the exact instance it's shot out of the cannon. Does that mean that if you checked the front of the bubble later on, the spray-paint wouldn't be there -- because the bubble at the instant it was spray-painted and at the instance it's checked somehow exist independently of one another?

The closest you could get would be a cannon that starts firing long in advance, emitting a fast-moving configuration of matter that evolves into later stages of the warp drive in reverse order (the earliest matter fired becomes the last stage of the warp bubble).

I see. So implicit in Alcubierre's work is the idea that the exotic matter would be *generating* the warp bubble. The warp bubble couldn't just be generated and continue to exist under its own power. It's a specific effect generated by and anchored to the exotic matter mentioned in the article. Am I correct?

Thank you very much for your time. I appreciate you answering my questions. --Brasswatchman (talk) 22:04, 23 May 2008 (UTC)

No problem.

Let's say, I don't know, someone spray-paints something on the front of the bubble the exact instance it's shot out of the cannon. Does that mean that if you checked the front of the bubble later on, the spray-paint wouldn't be there -- because the bubble at the instant it was spray-painted and at the instance it's checked somehow exist independently of one another?

Yes, except that I don't think you can spray paint the bubble in the first place; it's not an object. It can't have an outer hull or tubing for the exotic matter or anything like that, because such stuff would have to move (locally) faster than light. Here's a picture of the moving warp bubble and the past light cone of a point on its leading edge:

                         /    /
                       /    /
                     /    /
                   /    //\
                 /    / /  \
               /    /  /    \
             /    /   /      \
           /    /    /        \

The metric outside the bubble is Minkowski, so this light cone is really a cone. At the apex of the cone there's some exotic matter (the front of the warp bubble). We're assuming no FTL travel with respect to the local metric (otherwise the warp drive is superfluous), so the presence of that exotic matter can only be a consequence of events inside the light cone, and that doesn't include any part of the warp bubble at previous times. So it would seem to follow from basic physical assumptions that you have to actively introduce/induce exotic matter at each point along the path to keep the warp bubble going. In Alcubierre's geometry the exotic matter appears on its own, but it doesn't appear in response to the bubble's earlier motion, it appears because the metric we wrote down happens to require exotic matter appearing out of nowhere at that point. There are no physical laws (like a law of inertia) governing the evolution of the bubble over time.

Alcubierre's metric is very simple: outside the bubble is Minkowski space, inside the bubble is also Minkowski space but skewed with respect to the outside coordinates (deck-of-cards style, like a Galilean transformation), and to avoid discontinuity there's a thin boundary shell where the metric blends smoothly between the inside and outside. In the diagram above the limiting velocities are ±c outside the bubble, v ± c inside, and (f(x) v) ± c in between, where f(x) varies smoothly from 0 to 1 across the boundary (it's the same as the f in Alcubierre's paper). So it's pretty easy to draw all the light cones and work out what's causally connected to what. E.g. if you did try to spray paint the front of the bubble, the paint would necessarily (because of the local speed-of-light limitation alone) pass through the boundary of the bubble to the inside. It could remain indefinitely on the inside (along with the passengers), or it could leave out the back, but it couldn't get out to the front again. Nor, of course, could you see it from the front, since light can't get out either.

So implicit in Alcubierre's work is the idea that the exotic matter would be *generating* the warp bubble. The warp bubble couldn't just be generated and continue to exist under its own power. It's a specific effect generated by and anchored to the exotic matter mentioned in the article.

In Alcubierre's paper the warp bubble works essentially by magic. More realistically it would require active introduction of exotic matter from the outside in just the right way at every point along the path to keep the bubble going. Even more realistically there's no right way to do it because no form of matter having the necessary properties has been observed in the lab. -- BenRG (talk) 19:42, 25 May 2008 (UTC)

Please can anyone tell me why australia's earth is red?

Picklelilly (talk) 06:32, 20 May 2008 (UTC)

Look at Rock (geology) and Hematite--71.236.23.111 (talk) 07:20, 20 May 2008 (UTC)

I think it is because it has lots of iron in it. Bed-Head-HairUser:BedHeadHairGirl12:53, 20 May 2008 (UTC)

We also have a great Geology of Australia article. From there, I found maps from the Australian government's Geoscience division which document a whole lot of mineral deposits. These may help visualize the mineral distribution! Nimur (talk) 14:40, 20 May 2008 (UTC)

I wish to point out that not all of Australia's soil is red. The red colored soil in Australia is mainly due to the presence of iron oxide. 202.168.50.40 (talk) 02:53, 21 May 2008 (UTC)

See the Laterite article, and from Eyre, S. R. (1963). Vegetation and soils; a world picture. p. 255. OCLC 441202:

It is in those tropical regions with pronounced wet seasons alternating with definite seasons of drought that horizons of laterite are found extensively...because of climatic change, laterite can now be found in areas which are far too dry to permit laterite formation at the present time. These crusts are thus entirely fossil...

—eric 04:09, 21 May 2008 (UTC)

Stellar evolution and Sun

Per stellar evolution, Sun will become red giant in 5 billion years. However the luminosity of the Sun will increase by 10 percent over the next 1.1 billion years. Will civilization and higher group of land mammals become extinct only when Sun becomes red giant or within 1.1 billion years? What will be the effect on land animals/primates if luminosity of Sun increases by 10 percent? Otolemur crassicaudatus (talk) 13:14, 20 May 2008 (UTC)

A trivial calculation shows that, all else being equal, atmospheric temperatures would increase by 30C across the board. That would increase water vapor pressure by about a factor of 5 (in mmHg, at least), which would probably be catastrophic to land-based life. Sea-based life would certainly continue. Either way, these are incredibly slow changes, so evolution might work its way around such things. This is just my impression from some basic physics and little more. SamuelRiv (talk) 14:29, 20 May 2008 (UTC)

How do you get from +10% to 30C? The Stefan-Boltzmann law tells us that temperature goes as the 1/4 power of the radiative flux. So before we consider feedbacks +10% flux is only +2.4% in temperature which is more like 7 C. Feedback processes, like water vapor, will amplify that, but I think 30 C is an overstatement. Dragons flight (talk) 15:53, 20 May 2008 (UTC)

Earth#Future says the Earth is only expected to be habitable for about 500 million years. --Tango (talk) 15:03, 20 May 2008 (UTC)

I'm no expert, but maybe looking at those figures in perspective will help. The entire development from the first multicellular animals via dinosaurs to what we see now has taken less than 1.1 billion years or the 900 million years the article earth cites for plants disappearing. In the past 1.1 billion years, there have been several ice ages and "only" 200 million years ago all of earth's land mass was clumped together in one large continent Pangea. There have been five big and a couple of minor extinction events during the past 600 million years. This makes it kind of difficult to predict whether there are going to be land animals around and what land animals that would be. 71.236.23.111 (talk) 15:38, 20 May 2008 (UTC)

I think "habitable" in that context means habitable by humans - that's rather easier to predict, since we know what humans can survive. Life has a tendency to evolve to find ways of surviving in new environments, so I expect life in some form will go on much longer, but human life (without artificial means) won't be able to survive on Earth in 500 million years time (give or take). Of course, these are quite rough estimates and I don't think it would be too surprising if they turned out to be off by quite a large margin. --Tango (talk) 16:01, 20 May 2008 (UTC)

You're right Dragon - I forgot about SB and treating the Earth like a blackbody. My reasoning was just treating everything like a gas, which is quite silly now that I remember all those rules about how radiation transmits energy. SamuelRiv (talk) 16:24, 20 May 2008 (UTC)

Description of Human Being if last Ice Age didn't happen...

What would the human being be like if the last Ice Age didn't happen?--Vincebosma (talk) 14:44, 20 May 2008 (UTC)

See almost exactly the same question asked a few days ago: Wikipedia:Reference_desk/Science#What_if_the_Ice_Age_never_happened.3F! --Tango (talk) 15:02, 20 May 2008 (UTC)

But no one described what the human beings would be like --Vincebosma (talk) 15:08, 20 May 2008 (UTC)

No meaningful extrapolation can be made. Your best guess is likely as good as anybody else's. — Lomn 15:18, 20 May 2008 (UTC)

Couldn't someone just try? --Vincebosma (talk) 15:34, 20 May 2008 (UTC)

Super intelligent 30 foot tall creatures with razor sharp claws, gene manipulation has left them unable to reproduce through natural means so they are reliant on cloning to propagate the species, also they have lost the ability to feel love. Actually humans would probably not be much different its only history that would have gone much much differently since I don't think humans have changed that much physically since the last ice age, just culturally. -- Mad031683 (talk) 15:44, 20 May 2008 (UTC)

The last ice age is this ice age, since the polar ice hasn't melted yet, last I checked. We are in an interglacial. So what if there were no polar ice. What would you model the climate to be like? You could create a scenario of Neanderthals and Homo erectus not dying out. Would you keep them in a zoo? Paranthropus might still be around. Would your homo sapiens have left Africa? The scenarios are yours to play with. Read the articles follow the links and see what you can make fit. 71.236.23.111 (talk) 17:14, 20 May 2008 (UTC)

I disagree that humans wouldn't be that different. If it weren't for cold weather, the mammals wouldn't have thrived in the first place. I'm not sure how long ago we are talking about here when the questioner said "last ice age," but in general the average size of organisms in the biosphere increases with the average temperature. Dinosaurs and their neighbors were so big because it was so damned hot. When it got cold, small mammals started to dominate and we arose from them. No ice, no people. --Shaggorama (talk) 05:26, 21 May 2008 (UTC)

The Last glacial period was recent enough that Humans had already evolved to something very close (if not identical) to modern man, so it didn't play a major part in our evolution. It may, however, have played a major part in us thriving so well all over the world. --Tango (talk) 11:57, 21 May 2008 (UTC)

The world is a 'chaotic' system - in the sense of a butterfly flapping it's wings in China causing a tornado in Texas years later. The consequences of such a major hypothetical as a missing ice-age are quite literally unknowable. Could some tiny detail of changed human evolution caused us to wipe ourselves out with nuclear weapons during the cold war? Sure! Really, there is no rational answer to this. 71.155.164.147 (talk) 19:58, 21 May 2008 (UTC)

As the whole span of homo sapiens falls within the current ice age, it seems rather possible that without it there would be no humanity - just as there is no Homo sapiens idaltu. Xn4 02:42, 23 May 2008 (UTC)

Fluorescent lights degrade products on shelf?

I've always "heard" that for items that sit on the shelf for a while, fluorescent store lights degrade perishables that are in clear bottles/jars. When shopping for food (mayo, salad dressing, oils, etc) and heath items (vitamins, lotion, body wash, etc), I always select items near the back of the shelves (where it's dark and shadowed) Any truth to this? --70.167.58.6 (talk) 16:16, 20 May 2008 (UTC)

Not just fluorescent light, but any light in general tends to catalyze unwanted chemical reactions. (For a more extreme example, why do you think hydrogen peroxide is stored in brown bottles?) Of course, your idea doesn't work if the jars at the back of the shelf are older than those at the front. shoy 16:38, 20 May 2008 (UTC)

Consumer Reports magazine has reported for years that milk exposed to light will, at a minimum, develop "off flavors", hence the HP Hood Lightblock bottle. I expect it's true, to one degree or another, for many foods.

Atlant (talk) 17:02, 20 May 2008 (UTC)

The jars at the back should be newer - I believe pretty much all shops practice stock rotation. --Tango (talk) 17:58, 20 May 2008 (UTC)

Given that most bottles are plastic or cheap glass, there should be very little difference between fluorescent lights and incandescent lights having the same luminous intensity. People worry about the small amount of UV light in fluorescents, but the packaging should filter that. If a product is light sensitive, I would expect that it would react regardless of the type of lighting in the store. Dragons flight (talk) 18:09, 20 May 2008 (UTC)

Note that fluorescent and incandescent lights of the same luminous intensity will nevertheless have different spectra. Compare the essentially black body emission of an incandescent bulb (link) to the emission spectrum of a modern fluorescent lamp (link). Note that fluorescent lamps have sharp peaks down in the green (around 550 nm), whereas the emission of an incandescent lamp is brightest in the infrared.

The extra share of higher-energy green photons will drive some photochemistry that wouldn't happen under red light. Honestly, though, I'm not inclined to worry about it for items at the grocery store. You have no idea how things were stored before they got to the shelf, and a properly-managed store will rotate its stock (new products are added at the back) so that product at the front today isn't the product that was at the front yesterday. (In principle, then, you can get the freshest product by taking the stuff from the back—but that assumes that the store does rotate stock properly. It could be that the stuff at the back is the oldest on the shelf by a fair margin because the front items turn over regularly...then where are you?) I'd be more concerned for the very few items that demonstrate significant light sensitivity--like the aforementioned beer. TenOfAllTrades(talk) 19:26, 20 May 2008 (UTC)

It's well known that beer is light-sensitive. Too much light exposure leads to skunked beer. I would imagine other light-sensitive foods exist, but the details would vary depending on the chemical reactions involved. Friday (talk) 18:14, 20 May 2008 (UTC)

• My mother always takes from the back because less people would have picked it up and tampered with it. Now I know a better reason!Avnas Ishtaroth (talk) 01:41, 22 May 2008 (UTC)

Can natural oil ignite at normal temperatures?

A friends and I have argued after watching the film There Will Be Blood about whether or not oil can catch light without being heated. He argues that it is a common misconception that oil is highly flammable, and that it needs to be heated before it will ignite, though I disagree. Looking at the main oil article on Wikipedia I can't see a conclusive answer. —Preceding unsigned comment added by 81.137.213.177 (talk) 16:27, 20 May 2008 (UTC)

How would you ignite it without heating it? It's not likely to spontaneously burst into flames at room temperature, you would need to put a match to it or something. --Tango (talk) 16:31, 20 May 2008 (UTC)

How much you need to heat it will depend strongly on what oil you're talking about. Algebraist 16:42, 20 May 2008 (UTC)

Rumaging through my rusty ol' thinking box. You might have a look at Flash point, Combustion, Autoignition temperature, vapor pressure. What makes things go "boom" or "foomp" is released energy from rearranging chemical bonds. If you could use another reaction than oxidization, to break up the chemical bonds in your oil, you might be able to find something that works at room temperature and releases enough energy. That reaction might no longer qualify under "ignite" or "flamable". The finer the distribution of oil particles in your reactant the more efficient the reaction. Maybe someone else can help you develop this further. (Or tell you why it won't work.) --71.236.23.111 (talk) 18:12, 20 May 2008 (UTC)

I think that what the questioner is asking is what would happen if you simply dropped a match onto a pool of crude oil. Would it catch fire instantly like gasoline? Or would it take special effort to get it lit? APL (talk) 17:54, 20 May 2008 (UTC)

Crude oil is a mixture of all sorts of length of hydrocarbon chains. At a refinery they crack them into shorter ones and sort those by product. Assuming that your crude oil puddle hasn't been there for ages, it should still contain short chained hydrocarbons for immediate ignition. Don't try this at home, because the match will probably light the vapors above your puddle rather explosively. 71.236.23.111 (talk) 21:58, 20 May 2008 (UTC)

You really can't reliably light gasoline by dropping a lighted match into it. It's only the vapor that burns easily and if it's not in an enclosed space or sprayed out into an aerosol or something, gasoline is really rather reluctant to burn. 70.116.10.189 (talk) 22:57, 20 May 2008 (UTC)

Oil lamps were certainly the lighting of choice for quite a few of the previous centuries.

Many (many) summers ago, I did ceremonial work which involved lots of small flames here and there. The standard recipe was 6-oz metal juice can (yes, they were metal in those days), stuffed 3/4 full with cotton for the wick, and then filled not-quite-full with kerosene, same as #1 diesel today. Made a nice, flickery, not-too-hot, and definitely smoky flame.

To extinguish said lights, it was sufficient to poke the cotton wicking down below the surface of the kerosene -- it wouldn't burn without the wick. I think that brings us to the common thread here: be it wax, butter, animal fat, or other oil, the wick seems to be the key feature. The "heavier" products thus need at least sufficient heat to melt them enough to flow, mix with air, and burn.

-- Danh, 63.231.162.222 (talk) 23:15, 20 May 2008 (UTC)

The short answer is that most oils need to be either (a) heated or (b) atomized or (c) dispensed through a wick in order to burn. If you drop a lit match into a pool of oil (any kind of oil), the oil is unlikely to catch fire.

A nice way to atomize a natural oil and watch it catch fire is to hold a lighter or lit match next to some orange rind as you squeeze it. (An even nicer demonstration, in its way, is the Devil's Cocktail.) —Steve Summit (talk) 03:24, 21 May 2008 (UTC)

I hate to be anecdotal, but I can't find a good reference for this. I saw a thing on TV where some firemen were going to practice fighting oil fires by putting out a vat of burning diesel fuel. They had to use a propane torch to get it to start burning. Tossing a match into it would not have ignited it, I guess. Crude oil at the wellhead is another matter, though. I haven't seen the movie you mention, but I assume a gusher catches fire at some point. It is common knowledge that people who fight oil well fires live in fear of the spark that would re-ignite the gusher after they've blown it out with explosives. Crude contains lighter, more volatile hydrocarbons than does refined diesel, as was mentioned above, and the gusher itself aerosolizes the oil somewhat, I would imagine. --Milkbreath (talk) 10:45, 21 May 2008 (UTC)

Related question: In the video game The Darkness, there is one scene where the protagonist ignites money by pouring gasoline on it and shooting the money. I severely doubt this is possible, but is there any truth to it?Avnas Ishtaroth (talk) 01:44, 22 May 2008 (UTC)

DEFINITELY NOT! 71.155.164.147 (talk) 14:22, 22 May 2008 (UTC)

I agree it depends on the type of oil. Maybe you are referring to other types of oil, but some oils such as linseed oil can even self ignite if an oil soaked rag is left in the air.
— Apis (talk) 14:29, 24 May 2008 (UTC)

Weak Interaction Bosons

Hi there folks, I've been searching for a while now, and have been staggeringly unable to find the answer to my question (including on #physics at freenode); which of the W bosons mediate the electron capture, positron capture, neutron-neutrino, and anti-neutrino-proton collisions? More helpfully, and in general, where can I find Feynman diagrams for these fairly straightforward weak interactions?

Cheers! Carl Turner (talk) 16:37, 20 May 2008 (UTC)

Well, here are some beautiful suitable-for-framing Feynman diagrams for the interactions I think you're talking about:

    electron capture  positron capture   neutron-neutrino  antineutrino-proton

       |       |          |       |          |       |          |       |
     n ^   W+  ^ nu     p ^   W+  v nu     p ^   W+  ^ e-     n ^   W+  v e-
       |--->---|          |---<---|          |---<---|          |--->---|
     p ^       ^ e-     n ^       v e-     n ^       ^ nu     p ^       v nu
       |       |          |       |          |       |          |       |

The reason you can't find out whether it's the W+ or the W- is that the particle-antiparticle distinction doesn't make much sense for virtual particles. These are tree diagrams, so the W does have a well-defined four-momentum, and if it's timelike (which it won't always be) you could say that you "really" have a W+ or W- depending on which way the four-momentum points. E.g. in the first diagram if the neutrino's final energy is small enough then the electron momentum minus the neutrino momentum could be timelike and future-directed, in which case you could say that the electron "decays" into a W- and a neutrino and the W- collides with the proton turning it into a neutron. But it's a pretty dubious thing to say; you have to wonder why the electron happened to spontaneously decay when there was a convenient proton nearby to absorb one of the decay products, thereby making the decay possible in the first place. Also, these aren't the only Feynman diagrams for these processes, just the first-order contributions. It's better to think of the whole thing as a single interaction which involves the W field but not a W+ or W- particle. -- BenRG (talk) 18:35, 20 May 2008 (UTC)

Thanks a lot, those are the interactions I was describing, and I appreciate the clarification; and blame our educational system for talking in terms of virtual particles and not the fields/forces they represent. Oversimplification will be the death of us yet. Two further queries; by "first-order contributions", are you just making a distinction between quarks and hadrons? And secondly, is it justifiable to discriminate between the W bosons in the case of the beta decays? Given that they are usually illustrated with the interaction happening 'over time', i.e. with the following diagram, does this mean that the 'distance' the W- boson 'travels' is always time-like? I'll write this up for the articles shortly, and include the discussion in terms of space-time vectors, so I'd like to be clear.

Regards, Carl Turner (talk) 20:58, 20 May 2008 (UTC)

By "first-order contributions" I mean that there are many Feynman diagrams for these particular interactions and the ones I drew above are just the simplest ones. E.g. you could add a photon line between the electron and the proton in any of those diagrams and get a more complicated diagram with the same inputs and outputs, and that diagram also contributes to the overall amplitude of the interaction. There are also diagrams with more than one W. The different diagrams aren't different ways the interaction can happen, they're different "corrections" to the amplitude of the true, unique interaction, which is like a combination of all the diagrams. So this is another reason why it's problematic to talk about "the" W particle.

In the β^- decay diagram shown above the W always has a timelike momentum, but I still don't think it makes physical sense to call it a W- for the reasons I've already mentioned. You can't split the diagram into two separate events, the emission and subsequent decay of a W-, because there's not nearly enough energy in this situation to make a real W particle. The intermediate W is doomed to remain on the inside of the Feynman diagram, undetectable and ontologically ambiguous (since that isn't the only Feynman diagram).

On the other hand there's clearly a transport of charge going on here, it just isn't time ordered. In the electron capture diagram it seems fine to say that the intermediate W boson carries positive charge out of the nucleus or that it carries negative charge into the nucleus. Those are two descriptions of the same thing, whereas a real W+ moving to the right isn't the same as a real W- moving to the left. Even in the more complicated diagrams I think there will always be a W performing this "role", since there aren't any other Standard Model particles that can do it. So maybe you could play that up in the description. Or maybe it would just be confusing. I want to suggest something helpful here, but I don't think I understand QFT well enough.

You can probably ignore the fact that the nucleons are made up of quarks and gluons; there's no requirement that the particles in Feynman diagrams be fundamental (and who knows what's fundamental anyway?). Similarly you can deal with the proton and neutron being part of a larger nucleus by replacing the "p" and "n" with ¹³⁷
₅₆Ba
and ¹³⁷
₅₅Cs
or what have you. I don't know how one deals with the electron capture situation where the electron starts out orbiting the nucleus instead of coming in from infinity (which is the usual assumption for Feynman diagrams). -- BenRG (talk) 19:01, 21 May 2008 (UTC)

Francium reacting with water

If francium reacted with water, i know its not possible because it decays radioactively too quickly or something, what would the explosion be the equivalent of, a TNT blast? --Hadseys 21:47, 20 May 2008 (UTC)

This is rubidium, then caesium in water. At a guess, I'd say that the francium would scatter pieces of container into the four corners of the room. --Kurt Shaped Box (talk) 21:56, 20 May 2008 (UTC)

And what do you get once you've watch Kurt's video - the Francium Bomb Test in Water video :-)) Astronaut (talk) 22:39, 20 May 2008 (UTC)

Francium does not exist for long enough to be able to react with water due to its extreme instability. The video posted was a nuclear detonation test. Acceptable (talk) 23:47, 20 May 2008 (UTC)

Specifically, Operation Crossroads, shot Baker. --98.217.8.46 (talk) 00:26, 21 May 2008 (UTC)

Of course it was and I would hope the OP spotted that too - that's why there's a big smiley after the link. Astronaut (talk) 12:46, 21 May 2008 (UTC)

This source estimates the enthalpy of formation (that is, how much energy is released or required when making given amount) of francium hydroxide hydrates. Hopefully, one of our more chemically minded contributors can convert these into something more meaningful. Laïka 18:59, 21 May 2008 (UTC)

There are other effects that need to be considered. For example, if francium generates a hydrogen explosion so quickly it blows itself out of the water, you might get a series of small "pop"s as it bounces around on the water. Total energy released doesn't mean much if it's released over half an hour of bouncing around. --Carnildo (talk) 21:04, 21 May 2008 (UTC)